How one small text change in a study document can impact recruitment rates and follow-up completions

The validity and reliability of longitudinal research is highly dependent on the recruitment and retention of representative samples. Various strategies have been developed and tested for improving recruitment and follow-up rates into health-behavioural research, but few have examined the role of linguistic choices and study document readability on participation rates. This study examined the impact of one small text change, assigning an inappropriate or grade-8 reading level password for intervention access, on participation rates and attrition in an online alcohol intervention trial.

Participants were recruited into an online alcohol intervention study using Amazon's Mechanical Turk via a multi-step recruitment process which required participants to log into a study portal using a pre-assigned password. Passwords were qualitatively coded as grade-8 and/or inappropriate for use within a professional setting. Separate logistic regressions examined which demographic, clinical characteristics, and password categorizations were most strongly associated with recruitment rates and follow-up completions.

Inappropriate passwords were a barrier for recruitment among participants with post-secondary education as compared to those with less education (p = 0.044), while grade-8 passwords appeared to significantly facilitate the completion of 6-month follow-ups (p = 0.005).

Altogether, these findings suggest that some linguistic choices may play an important role in recruitment, while others, such as readability, may have longer-term effects on follow-up rates and attrition. Possible explanations for the findings, as well as, sample selection biases during recruitment and follow-up are discussed. Limitations of the study are stated and recommendations for researchers are provided.

ClinicalTrials.gov NCT02977026. Registered 27 Nov 2016.